Negative creep gasket with core of shape memory alloy

Abstract

A negative creep gasket with core of shape memory alloy to ensure a leak-tight, automatic and continuous multiple seal of critical plat/piping systems comprises a corrugated core manufactured from shape memory alloy and shape-memorized in advance to the “swelling” under conditions of rigidly fixed corrugation followed by aging under temperature significantly greater than temperature of austenite state of the shape memory alloy. Temperature interval of reverse martensitic phase transformation of the shape memory alloy is close to process temperatures of the assembly. Negative creep effect of the gasket results from shape-recovering stresses that appear between rigid flange surfaces and deformed by bolt preload corrugation during constrained shape recovery of the gasket core under conditions of a variety of operating temperatures and internal pressures.

1 . A gasket with core of shape memory alloy having a feature of negative creep effect and providing leak-tight, automatic and continuous multiple seal of critical plant/piping systems under a variety of operating temperatures and internal pressures.  
   
   
       2 . A gasket according to  claim 1  wherein said multiple seal results from corrugated gasket core encapsulated by protective envelope manufactured from materials convenient for specific operating conditions such as fires, oxidation, chemical influences, and others.  
   
   
       3 . A gasket according to  claim 1  wherein said negative creep effect of the gasket results from reactive shape-recovering stresses that appear between gasket corrugation deformed by bolt preload forces and rigid flange surfaces under conditions of a variety of operating temperatures and constrained shape recovery of deformed gasket corrugation.  
   
   
       4 . A gasket according to  claim 2  wherein said shape memory alloys have temperatures of reverse martensitic phase transformation that are close to operating temperatures of the assembly.  
   
   
       5 . A gasket according to  claim 2  wherein said corrugated gasket core is combined with additional non-corrugated portion of the gasket manufactured from the same shape memory alloys with the same protective envelope or from conventional gasket materials, and located on inner edge of the gasket.  
   
   
       6 . A gasket according to claims  3  and  5  wherein said reactive shape-recovering stresses have direction inverse to the direction of operating creep providing gasket “swelling”.  
   
   
       7 . A “forced fixation technique” to fabricate corrugated gasket core while deforming a flat ring of the shape memory alloy to obtain a stress-induced martensite under conditions of temperature of martensite state and rigidly fixed corrugation followed by aging obtained and rigidly fixed corrugation under temperature significantly greater than temperature of austenite state of the shape memory alloy with subsequent release the corrugation from rigid fixation under temperature of martensite state.